Fuses are commonly used in integrated circuits to provide redundancy and programming capabilities. To increase yield in integrated circuits such as memory chips, it is common to include redundant memory cells on the memory chips. If a memory circuit is found to be defective or is not needed, the fuse may be blown by activating or deactivating the redundant memory cells. Another common practice is to utilize fuses to program or customize integrated circuits for a particular application or customer. In this manner, the same chip may be produced and customized for individual customers by programming the fuses after fabrication, thereby reducing the fabrication costs.
Typically, fuses comprise a conductive link that may be blown or ruptured to prevent current from flowing. The conductive link is typically formed of a metal, such as aluminum or copper, and blown by a laser. The use of the laser, however, requires complicated processing steps and expensive laser equipment.
Another type of fuse involves the use of an electrical fuse. Generally, an electrical fuse comprises two endpoints or contact pads connected with a thinner link, referred to as a fuse link. The electrical fuse is formed from a layer of polysilicon that has been deposited on a silicon substrate and silicided. In operation, the smaller dimensions of the fuse link causes high current concentrations or “current crowding” where the dimensions of the fuse are reduced in the fuse link. To program or “blow” the fuse, an electrical current of sufficient magnitude is passed through the fuse link for a sufficient period of time to cause silicide agglomeration or melting of the fuse link, thereby increasing the resistance of the link. A sensing circuit is then able to sense the amount of resistance to determine the state of the fuse.
In recent years, silicon-on-insulator (SOI) substrates have been investigated for use in semiconductor processing. As the use of SOI substrates increases, it is necessary to develop new process steps and devices to incorporate aspects of the SOI substrates. In particular, new processes are needed to incorporate the use and fabrication of an electrical fuse into existing SOI fabrication processes. For the processes to be effective and useful, the processes should be integrated with existing processes, adding no or few additional process steps.